1. Technical Field
The present invention relates to an image display apparatus and an image display system.
2. Related Art
There has been a known image display system (stereoscopic video image display apparatus) including an image display apparatus that displays an image and a pair of shutter glasses worn by a viewer and allowing the viewer to stereoscopically view the image displayed by the image display apparatus through the shutter glasses (see JP-A-2009-232249, for example).
FIGS. 7A to 7C describe the operation of an image display system of related art.
Specifically, FIG. 7A is a timing chart showing the timing when image data are written along each scan line produced by an image display apparatus, and the vertical axis corresponds to the vertical direction of the image display apparatus (the vertical axis represents the positions of the uppermost scan line L1 to the lowermost scan line Ln). FIG. 7B is a timing chart showing the timing when the states of a shutter for the left eye (lower part of FIG. 7B) and a shutter for the right eye (upper part of FIG. 7B) that form shutter glasses are switched between a light transmitting state OP and a light blocking state CL. FIG. 7C shows an image visually recognized through the shutter glasses during a second period T2.
In FIG. 7A, to diagrammatically show the timing when image data are written along the scan lines L1 to Ln, a straight line is drawn to connect a write start timing (update start timing) Ws, when image data start being written along the scan line L1, to a write end timing (update end timing) We, when the image data stop being written along the scan line Ln. It is noted that images displayed by the image display apparatus are labeled with characters as follows: An image for the left eye is labeled with “L”; an image for the right eye is labeled with “R”; and a black image is hatched (a parallelogram area represents each of the images described above) for ease of description.
The image display apparatus described in JP-A-2009-232249 is formed of a liquid crystal display that displays an image in a line sequential drive scheme. The liquid crystal display writes image data sequentially from the uppermost scan line L1 to the lowermost scan line Ln during each of vertical scan periods Tv1 to Tv4, which are specified by a vertical sync signal to update a displayed image, as shown in FIG. 7A. The liquid crystal display updates the displayed image during a first period T1 (vertical scan periods Tv1 and Tv2) and a second period T2 (vertical scan periods Tv3 and Tv4), which are alternately switched therebetween. Specifically, the displayed image is switched to an image for the left eye and a black image in this order during the first period T1, and the displayed image is switched to an image for the right eye and another black image in this order in the second period T2.
Each of the shutter glasses (shutter for left eye and shutter for right eye) described in JP-A-2009-232249 is formed of what is called a liquid crystal shutter. The shutter glasses are so configured that the state of the shutter for the left eye is switched to a light blocking state CL, in which substantially the entire amount of light is blocked, and the state of the shutter for the right eye starts being switched to a light transmitting state OP, in which substantially the entire amount of light is transmitted, at a switching point P when a first period T1 is switched to a second period T2, as shown in FIG. 7B. The shutter glasses are further so configured that the state of the shutter for the left eye starts being switched to the light transmitting state OP and the state of the shutter for the right eye is switched to the light blocking state CL at a switching point P when a second period T2 is switched to a first period T1.
That is, inserting a black image between an image for the left eye and an image for the right eye prevents images for the left and right eyes from overlapping with each other and allows the viewer to visually recognize the displayed image (image for left eye and black image) only with the left eye during a first period T1. The viewer then visually recognizes the displayed image (image for right eye and black image) only with the right eye during a second period T2. The viewer therefore stereoscopically views the displayed images with the aid of parallax.
Since each of the shutters for the left and right eyes relies on the liquid crystal technology, there is a light blocking to transmitting transition period TD1 resulting from the response speed of liquid crystal molecules, a period required to achieve the light transmitting state OP after the state of the shutter starts being switched to the light transmitting state OP, as shown in FIG. 7B.
Similarly, there is a light transmitting to blocking transition period TD2, a period required to achieve the light blocking state CL after the state of the shutter starts being switched to the light blocking state CL.
Since the light blocking to transmitting transition period TD1 and the light transmitting to blocking transition period TD2 are present, for example, at the start and end of a second period T2, the transmittance of the shutter for the right eye becomes lower than that in the other periods.
An image visually recognized through the shutter glasses during the second period T2 therefore has the following problem: The brightness of upper and lower areas Ar1, Ar2 is lower than that of the other areas due to the light blocking to transmitting transition period TD1 and the light transmitting to blocking transition period TD2, as shown in FIG. 7C. That is, the visually recognized image suffers from brightness unevenness. An image visually recognized through the shutter glasses during a first period T1 has the same problem.